This invention relates to body armour of the type which can be worn to protect the wearer from a high speed projectile such as a bullet from a handgun or rifle.
Body armour must be capable of stopping passage of bullets of a variety of sizes and speeds, and it must also reduce the damage caused by the impact resulting from the bullet being trapped within the armour. Moreover, to be acceptable as body armour, it must be flexible without gaps and of light weight.
In a commonly used type of body armour, the material used in an outer bullet-trap essentially consists of an array of multi-layered flexible slabs or platelets formed of hard material and joined by tough flexible cloth so as to provide a discontinuously flexible garment. Such body armour has the advantage of the immediate post-impact velocity of the platelet containing the bullet being predictable for a chosen platelet mass and an anticipated bullet threat because the collision of the bullet with a platelet is inelastic. On collision of the bullet with the platelet, the velocity of the platelet relative to the bullet velocity is simply proportional to the ratio of the bullet mass (m) to the post-collision mass of the platelet (M) plus the bullet mass, i.e., (M+m). It is apparent, therefore, that for a particular bullet threat that the post-collision velocity of the platelet, i.e., the maximum possible platelet velocity just before its collision with a backing component of the garment must be preset at an acceptable level, and this is done by choosing a sufficiently large platelet. In summary, in the platelet type of body armour, the trap portion of the device converts the penetration threat of a high-velocity, low-mass, small-diameter soft bullet into the bruising impact threat of a low-velocity, high-mass, large diameter hard-fronted rigid body. A pronounced rigid bulge occurs on the inner surface of the impacted platelet arising from it being hit with the bullet and its effect on any backing component of the garment is equivalent to a vigorous blow from a large hammer. It appears that known backing components are not capable of dealing with such a blow without the wearer suffering from bad bruising or bone fracture. Moreover, because flexibility is imperative, the closeness of the platelets is limited, and in sharply curved areas of the body, gaps between adjacent platelets may be sufficiently large to allow bullet penetration. Additionally, the required rigidity of each individual platelet can result in spalling, that is the breaking of the platelet into massive, hard, jagged fragments which may penetrate the inner component because the velocity of the spall may approach that of the striking bullet.
The use of hard spheres has been suggested in the prior art. Canadian patent No. 797,509, Oct. 29, 1968, to King, shows hard spheres embedded in rigid plastic plates. U.S. Pat. No. 4,186,643, Feb. 5, 1980, to Clausen, also discloses a flat panel laminate and refers to the use of glass beads which are fixed in place for effectively abrading a projectile. In U.S. Pat. No. 3,324,768, June 13, 1967, to Eichelberger, there are shown rigid panels of hard plates having a layer of glass balls or marbles. U.S. Pat. No. 4,179,979, Dec. 25, 1979, discloses hard spheres supported by material of high tensile strength with the spheres being restrained in place by a material such as foam or a suitable resin intermixture. In U.S. Pat. No. 3,705,558, issued Dec. 12, 1972, to McDougal et al, there is also shown an armour in which hard spheres are encased in a metal container which has a non-flexible backing of a material such as aluminum. As will be explained in more detail below, these type of armour structures do not provide the same energy absorbing characteristics of the present invention.